1. Field of the Invention
This invention relates to a rotary fluid pump having a magnetically suspended and rotated impeller and a method of making the same. More particularly, this invention concerns a rotary fluid pump comprising a housing, an impeller having magnetic impeller blades, a stator member attached to the housing, means for levitating the impeller such that the impeller is substantially centered within the housing, and means for rotating the impeller, and wherein the geometric configuration of the rotary fluid pump is sized and proportioned to minimize stagnant and turbulent fluid flow.
2. Description of the Related Art
The use of a rotary pump ventricular assist device for aiding a patient's heart in pumping blood is well known. The rotary pump ventricular assist device may be connected to the patient's heart in a left-ventricular assist configuration, or a right-ventricular assist configuration, or a bi-ventricular assist configuration. For instance, if the left-ventricular assist configuration is adopted, the rotary pump is connected between the left ventricle of the patient's heart and the aorta. Generally, the rotary pump comprises a housing having an inlet and an outlet, an impeller positioned within the housing and having impeller blades, and a stator member. The blood enters the inlet of the housing and is pumped by the rotating impeller through the housing to the outlet and into the patient's circulatory system.
Artificially pumping blood utilizing a rotary pump may be detrimental to the blood. If the rotary pump is inefficient, the pump will impart excessive entropy to the blood which usually takes the form of heat or fracture. The heat produced from the pump can damage the blood. The blood cells may coagulate or the albumin of the blood may denature if the temperature reaches forty-two degrees centigrade (42.degree. C.).
Moreover, numerous studies have proven that exposing blood to high stresses results in direct or delayed destruction of blood. As a result of the rotation of the impeller, regions of turbulence, jet formation, cavitation and rapid acceleration may be created and cause the blood cells flowing through the pump to break down and rupture. Also, the geometric configuration of a rotary pump may contribute to regions of retarded flow being formed, such as, recirculation and stagnation which cause blood to deposit on the pump structure resulting in thrombosis.
Many attempts have been made to overcome the above-mentioned disadvantages of utilizing a rotary pump as a ventricular assist device. One type of conventional rotary pump utilizes mechanical bearings that necessitate a lubricant flush or purge with an external lubricant reservoir for lubricating the bearing and minimizing heat generation. Examples of this type of rotary pump are illustrated in U.S. Pat. Nos. 4,944,722 and 4,846,152 issued to Carriker et al. and Wampler et al., respectively. There are many disadvantages to this type of rotary pump. The percutaneous supply of the lubricant purge fluid degrades the patient's quality of life and provides a potential for infection. Seals for the external lubricant are notoriously susceptible to wear and to fluid attack which may result in leakage and the patient having a subsequent seizure. Also, an additional pump is needed for delivery of the lubricant to the bearing. Yet another disadvantage of this type of rotary pump is that the bearings will need to be replaced over time because of wear due to the bearings directly contacting other pump structure.
In order to eliminate the need for an external purge of lubricant, a rotary fluid pump having a magnetically suspended impeller was created. By utilizing a magnetically suspended impeller, direct contact between the bearing and other pump structures, as well as external lubricant purges are eliminated. Examples of this type of rotary fluid pump are disclosed in U.S. Pat. Nos. 5,326,344 and 4,688,998 issued to Bramm et al. and Olsen et al., respectively. This type of rotary pump generally comprises an impeller positioned within a housing, wherein the impeller is supported and stabilized within the housing by a combination of permanent magnets positioned in the impeller and the housing and an electromagnet positioned within the housing. The impeller is rotated by a ferromagnetic stator ring mounted within the housing and electromagnetic coils wound around two diametrically opposed projections. The ferromagnetic impeller and the electromagnetic coils are symmetrically positioned with respect to the axis of the rotary pump and thus, impose an axially symmetric force on the fluid passing through a single annular gap formed between the housing and the impeller. The disadvantage of this type of rotary pump is that there is only one annular gap for the blood to pass through and it serves competing purposes with respect to fluid flow and the magnetic suspension and rotation of the impeller. Regarding fluid flow, the gap is desired to be large for efficient pumping whereas, for efficient suspension and rotation of the impeller, the gap is desired to be small. In this type of rotary pump, the fluid gap is relatively small and does not allow for efficient pumping of blood therethrough which may result in the destruction of blood cells.
The pursuit of designing a rotary pump which is sized and proportional to satisfy the competing requirements of providing satisfactory hydrodynamic performance and blood bio-compatibility, as well as efficient magnetic levitation and rotation of the impeller, involves the manipulation of numerous design parameters, arguably more than the human designer can manage at one time. The conventional process for designing a rotary fluid pump limits the focus of the design parameters and relies heavily on first order principles, such as Bernoulli's equation and Euler's equation, empirical analyses and trial-and-error methods. A prototype of a pump design based substantially on intuition is created and subjected to testing. Only when a fluid exhibiting the characteristics of blood is pumped through the prototype pump is it clear whether the design is viable. Because the cost of building a prototype is usually high and typically multiple prototypes are created and tested before a final, viable pump is completed, the process can be quite expensive and time-consuming. Furthermore, the best design of the infinite number of options is not guaranteed using this process.
Nowhere in the cited related art is there disclosed or suggested a rotary pump for pumping blood through a patient having a magnetically suspended and rotated impeller, wherein the geometric configuration of the pump provides for blood flow that is hydrodynamically and bio-compatibly satisfactory and a method of making the same. Therefore, there is a definite need for a rotary pump having a magnetically suspended and rotated impeller that pumps fluid without creating regions of stagnant and turbulent fluid flow and a method of making the same.